1. Field of the Invention:
The invention relates to a bogie for a railway vehicle.
2. Related Art:
Bogie constructions currently used in railway vehicles such as engines and cars or other similar vehicles are usually such that the body construction of the bogie is stiff with the wheel sets affixed to it. A stiff bogie body entails many drawbacks, one of the most significance of which shows up when moving through curves. Since the bogie body is stiff, the wheel sets of the bogie are not able to move radially in the curve, causing the wheels of the set to wedge against the rails which causes extreme wearing of the wheels and rails. Such a wedging makes e.g. a part of the engine's pull force "vanish" in the curve resistance. Riding through curves with such a railway vehicle with a stiff body is possible only by using an axial clearance between the bearing housing and the bogie body (construction type Y25). When driving straight, this kind of bogie construction behaves well, but in curves it will "push" as described above. The construction can be modified by making the wheel sets clearly self-steering with each axle adapting to the direction of the rails regardless of the other axles (construction 65sd). Said construction functions well with small speeds both in curves and when riding straight, but when the speed increases, a vibration (so called hunting) will occur around the vertical line against the centre line of the axle. This makes the use of such bogies unstable and even dangerous when riding with high speeds.
Various solutions have been tried in order to avoid the drawbacks described above. For example, in the publications FR-76296, US-4 478 153, EP-165752, EP-161729 and US-3 528 374, different bogie constructions have been described where the bogie body has been divided into two parts and articulated in the middle so that the wheel sets are able to rotate with respect to each other and thus follow the curves according to the curve radius, i.e. radially. Typical to all radially controlled bogie constructions is that they are explicitly steered on the basis of the curve radius when the steering is based e.g. on the mechanical observation of the angle difference between the bogie and the car body and on the conversion of the angle difference to an angle difference of the two bogie parts equivalent to the curve radius. Generally it is a question of a mathematical problem of changing a known quantity into another prescribed quantity. Only the mechanisms, with which this is carried out in the said publications, differ from each other. These constructions have a drawback of making the constructions complicated, expensive and heavy, as can be seen in the said publications. E.g., in the publication FI-76296, a rod connecting the bogies prevents the efficient use of the space between the bogies for loading. When using a fluid coupling of the publication US-3 528 374 between the bogies, the said space can be exploited, but the construction will be expensive to service and will damage easily.
When using the construction of 4 478 153 where the sets of wheels are not mechanically controlled, but are allowed to be steered by elastic elements, the characteristics lie somewhere between the mechanically controlled bogies and freely controlled sets of wheels. By extending the axial distance of the bogie, a better riding stability can be achieved, but the bigger bogie size will take otherwise usable space between bogies.
If it is desirable to make the loading space of a freight car as big as possible, the bogies must be built as short as possible, which means that the riding characteristics will become worse or that the steering of the bogie parts will become more complicated. When it is desired to maximize the transport space, the supporting constructions of the car must be made as small as possible, which would require extending the side frames to the sides of the bogie. This again means that, deviating from the traditional practice, the bearing and cushioning of the bogies must be made inside the wheels. Even if the side frames were not extended to the sides of the bogie, concerning the articulated two-part bogies, at least the cushioning must be placed inside the wheels, because loading through the springs must be brought in vertical plane through the axial line of the wheels in order to avoid moment in the bogie joint or to avoid an extremely complicated construction. As a result of this, the car itself will lean considerably in the curves since the bearing distance of the springs will narrow in the lateral direction of the car.
The above-mentioned problems will still become emphasized in situations occurring frequently in railways, i.e. in situations where, because of the roughness of the railway e.g. one of the bogie wheels rises higher or falls lower than the other wheels; this can happen e.g. on railway yards at gearings or when approaching a curve (when the outer rail of the curve will rise with respect to the inner rail) or when leaving a curve (when the outer rail will fall with respect to the inner rail). The two parts of the bogie will then twine with respect to each other about the longitudinal axis of the car. Additionally because of the turning by the curve and the tendency to incline caused by the centrifugal force, it must be stated that no known solution provides a satisfactory riding result. It can of course be imagined that the technical knowledge of the various publications, e.g. the inclination suppressor of DE-2 422 825, be connected to the said bogie constructions. In principle, it should then be possible to achieve a functional construction, but it would be so complicated, heavy, demanding of a lot of service and expensive that it would not be realistic.